1. Field of the Invention
The present invention relates to a system for inspecting chips, and more particularly, to a system for inspecting chips in a tray.
2. Description of the Related Art
Due to the compact and high performance requirement of electronics, the technologies of both integrated circuit (IC) design and manufacturing, as well as IC packaging, are advancing steadily. In the case of liquid crystal display (LCD) technology, for example, when a WXGA LCD is introduced by replacing a VGA LCD, the display panel circuitry becomes more complex due to the higher resolution. If the number of LCD driver ICs is not increased, every LCD driver IC must have more pins or ports. Under such circumstances, COF (Chip On Film) or COG (Chip On Glass) bonding techniques are gradually becoming more popular than TAB (Tape Automated Bonding) technique for this type of technology development. In directly attached to the electrode pads of the LCD panel, which can reduce tape cost. The cost of TAB tape is high, more than 70% of the total packaging cost. Therefore, the cost advantage of COG bonding technique is very appealing. Although COG bonding technique has cost advantage, the manufacturer still cannot substitute COG bonding technique for TAB technique. This is due to the fact that in the COG technique the driver ICs are directly mounted onto panel glass, making rework very difficult in cases where a driver IC has a driving problem. The problematic driver IC must be removed from the panel glass, and this process is very troublesome. Improved inspection of driver ICs prior to bonding is a key step to improve the efficiency, and thus the popularity, of the COG technique.
In wafer packaging technology the gold bumps on a chip are inspected at the wafer level; many testing-equipment producers offer products to automate steps of this inspection process. After gold bump inspection, the chips may be damaged or contaminated between the dicing process and the final test, and there is currently no process for inspection of every chip among these steps. At present, statistical process control procedures are used to monitor the quality of chips. Because not every chip is inspected after gold bump inspection, the production yield is difficult to control, which affects the willingness of producers to adopt the COG technique.
The first problem to be overcome while inspecting diced chips in a tray is how to perform the chip focusing. A tray is usually a plastic injection molded product. As plastic molded products often suffer warping or deformation, they often have imprecise dimensions. As a result, the chips in a tray will fluctuate in height or lie at an angle, creating problems for an automated chip inspection system. A common solution to the height fluctuation is coarse and fine focus adjusting mechanisms. That is to say, the height of a chip will be brought into focus by the coarse focus mechanism, which has wider depth of focus and lower magnification capabilities, and then the height of the chip will be further adjusted by the fine focus mechanism, which has higher magnification capabilities and narrower depth of focus. Finally, the chip can be inspected under high magnification. This solution suffers from slow throughput and cannot meet the requirements of the packaging industry, as it is not suitable for continuous high-speed inspection situations.
The present invention proposes a solution, which can directly inspect chips in tray at high throughput rates, for the above problems and the urgent requirement of the chip packaging industry.